Device for separating suspended material from a fluid stream by specific gravity difference

ABSTRACT

A tube settler improves separation performance by dividing flow path of a fluid to be treated into a multiplicity of tubular passages to achieve fluid stream commutation and to reduce the distance which a suspended particle has to fall increasing a settling area. A critical upward-flow rate for avoiding obstructions to precipitation of the suspended particle without turbulence depends on the cross-sectional configuration of the tubular passage. A tubular passage of triangular, circular, hexagonal or rhombic configuration is disadvantageous because the height or distance from top to bottom differs from part to part across the vertical section of the passage. 
     This invention provides a tube settler or multitube separator having a tube-nest assembly for passing the fluid to be treated therethrough. And, inclined tubular passages of the tube settler are an approximate boomerang cross-section.

This is a division of application Ser. No. 830,697, filed Sept. 6, 1977now U.S. Pat. No. 4,122,017 issued Oct. 24, 1978.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus to be employed in thetreatment of fluids, particularly water, sewage, waste water and thelike, for separating suspended particles of foreign matter from thefluid being treated which contains such suspended particles by takingadvantage of the difference between the specific gravity of suchsuspended particles and that of the fluid. More specifically, theinvention relates to a multitube separator wherein an assemblycomprising a multiplicity of long and narrow tubular passages of acertain cross-sectional configuration arranged compactly and parallel toone another under a certain systematic cross-sectional alignment ispositioned in an inclined relation to the horizontal, through whichtube-nest assembly the fluid being treated is allowed to pass, wherebythe occurrence of a turbulence is prevented which hinders the settlingof suspended particles from the flow of the fluid being treated andwhereby the distance which a suspended particle in the fluid must falluntil it reaches the bottom of the passage. The purpose of the tube-nestassembly is to obtain improved results such as reduced time forseparation, increased clarity of the separated fluid, and increasedtreatment capacity, and also to provide a more compact apparatus. Theinvention provides a multitube separator of novel and improved designwhich further improves said improved results and also gives variousother advantages.

This type of multitube separator can be employed for the settling andseparation of suspended particles having a greater specific gravity thanthe fluid to be treated or for the floating and separation of particleshaving a smaller specific gravity than the fluid, whichever the case maybe. Suspended materials are often in the form of fine solid particles.Beside the case with such suspended materials, the separator can be alsoemployed for separating immiscible fluids, e.g., oil from water.However, for the purpose of simplification and better understanding,description is made hereinafter mainly with respect to the case wherefine solid suspended particles having a greater specific gravity thanthe fluid being treated are settled and separated from the fluid.

A settling and separating device having above said type of multitubeseparator is hereinafter referred to as a tube settler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a typical suspended-materialseparating apparatus employing a tube settler including the deviceaccording to this invention.

FIG. 2 illustrates the configuration of a tube passage in the tubularpassage assembly according to this invention.

FIG. 3 is a bird's eye view of the tubular passage assembly according tothis invention.

FIG. 4 is an end view of the flow passage ends in the tubular passageassembly according to this invention.

FIG. 5 is a graphic chart of test results showing the relation ofeffluent turbidity and upward flow rate for various tubular passageshaving various different cross-sectional configurations.

FIG. 6 is a bird's eye view of a corrugated sheet of which the tubularpassage assembly of this invention is made.

FIG. 7 is an end view of the flow passage ends of two tubular passageassemblies to be jointed together in crosswise direction, with theopposed side ends thereof shown side by side.

FIG. 8 is an end view of the flow passage ends of the two tubularpassage assemblies of FIG. 7 connected together in lateral direction.

FIG. 9 is an end view of the flow passage ends of the two tubularpassage assemblies of FIG. 7 connected together laterally in the mannerdifferent from FIG. 8.

FIG. 10 is a bird's eye view of a corrugated strip used in theconnection with two assemblies in FIG. 9.

FIG. 11 is a vertical section of an inclined tubular passage including avertical portion.

FIG. 12 is a vertical sectional side elevation of a tubular passageshowing a modified effluent end of the passage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical example of the tube settler. However, it is to beexpressly understood that the scope of the invention is not limited tosuch example. Referring to FIG. 1, raw water containing suspendedparticles is mixed with a chemical coagulant such as aluminumpolychloride or alumina sulfate, stirred, and the mixture is introducedinto a flocculator tank 1 wherein coagulant flocs adhere to suspendedparticles to form large precipitatable particles of greater specificgravity. The water thus flocculated is led to the influent end of a tubesettler assembly shown generally as 2. The tube settler assemblycomprises a multiplicity of long and narrow tubular passages having aselected cross-sectional configuration aligned parallel under a certainsystematic cross-sectional arrangement and inclined at an angle a to thehorizontal. Said water flows slantingly and upwardly through the tubularpassages in the tube settler and meanwhile the flocs adhering tosuspended particles are settled. Said angle a is greater than the angleof repose of the precipitate, so that the precipitate is allowed to flowdown over the bottom of the tube counter to the flow of fluid. Dischargeat the influent end of the tube settler, the precipitate is accumulatedin the lower portion of a sludge collection tank 3 for periodic orcontinuous removal therefrom. The clarified fluid effluent from the topend of the tube settler is collected in a vessel (4) and is led awaytherefrom.

As described above, generally a tube settler provides improvedseparation performance through the division of the flow path of the rawwater into a multiplicity of tubular passages, because such divisionimproves fluid stream commutation, reduces the distance which asuspended particle must fall, and increases the settling area.Conventionally, the cross sectional configuration of the tubularpassages of a tube settler has been such as circular, square,triangular, hexagonal, or rhombic. These shapes give no muchsatisfactory results for several reasons. A tubular passage oftriangular, circular, hexagonal or rhombic shape has a disadvantage inthat its height or distance from top to bottom differs from part to partacross the vertical section of the passage. Accordingly, the distancewhich a suspended particle in the fluid must fall until it reaches thepassage bottom varies depending upon where it is located. This leads touneven precipitation and thus hinders effective utilization of thesettling area within the tube. In a tubular passage of square crosssection or triangular cross section wherein one side surface forms thebottom, the precipitate lies in a thin layer and has a relatively highsurface area exposed to the fluid passing through the tube. This meansrelatively low gravitational forces effected on the precipitate forslip-off and relatively large frictional resistance, and it is likelythat some of the precipitate is resuspended by a fluid stream runningopposite to the direction of slip-off. Circular or hexagonal shape doesnot give sufficient concentration of precipitated matter either. Apassage of chevron cross-sectional configuration disclosed in theJapanese Patent Public Disclosure No. 46-7436 provides uniform height,or uniform distance for precipitation across the vertical sectionthereof irrespective of where suspended particles are located; theprecipitate is allowed to collect in a thick layer in the center of aV-shaped bottom of the passage.

In order to obtain effective settling and separation of suspendedparticles from fluids, turbulence must be avoided. The settling ofsuspended particles is substantially hampered under the condition ofturbulence. The commonly used tube shapes other than said chevroncross-sectional configuration have a relatively high hydraulic radius,and the resulting Reynolds number for flow of a fluid through the tubepassages is relatively high. Thus, with the commonly used tube shapes,it is necessary that the flow rate or through-put rate of fluid must below in order to keep Reynolds number below the critical Reynolds numberand to avoid turbulent flow. Accordingly, the critical upward-flow ratefor avoiding obstructions to precipitation without turbulence isgoverned by the cross-sectional configuration of the tube passage; andwith tube passages of the commonly used shapes, except said chevroncross-sectional configuration, the critical upward-flow rate isgenerally low. The hydraulic radius of said chevron cross-sectionalconfiguration is low and the critical rate of upward flow through thepassages of said configuration is high; so, chevron cross-sectionalconfiguration increases the treating capacity of the tube settler.

It is an object of this invention to provide an improved cross-sectionalconfiguration for the tubular passages of a tube settler, with overalladvantages over the cross-sectional configurations disclosed in theprior art. The above said chevron cross-sectional configuration has beenbelieved to prove more advantageous as a tube shape than any othercross-sectional configuration from a geometrical point of view, and infact, exhibits good performance as such. In industrial application,however, it has been found that said configuration still involves aproblem requiring reconsideration in relation to the effect of aboundary layer in the flow rate profile in the cross section of a tubepassage. The flow rate of a boundary layer which develops along thepassage wall as fluids flow ranges from free to zero. The boundary layerdecreases the average flow rate of fluids passing through the tube. Froma different point of view, it makes the effective sectional area of thetube smaller than the geometric sectional area thereof. If the crosssection of a tube passage presents a zone surrounded by two contourportions intersecting at an acute angle, the boundary layer along thecontour portions is apt to grow thicker, resulting in decreased averageflow rate. It is a motive for this invention to eliminate the acuteangle zone present in a chevron cross-sectional configuration under thelimitation of certain systematic tube-passage alignment and withoutprejudice to the uniformity of settling distance and goodsludge-collecting function. Other objects of this invention will becomeapparent fully from the following detailed description, and they includethe provision of various other improvements.

The cross-sectional configuration of the tubular passages of a tubesettler according to this invention and the configuration of a tube-nestassembly composed of the passages are described below.

The tubular passages 5 of the tube settler according to the presentinvention are of an approximate boomerang cross-sectional configuration.As illustrated in FIG. 2, the cross-sectional configuration of a tubularpassage 5 comprises two long sides 6 and 6' of equal length buttedend-to-end so as to define a certain included angle b upwardly, saidlong sides forming a bottom wall, two inclined sides 7 and 7' of equallength, each extending from the other end of one of the long sides 6 and6' in parallel relation to the other of the long sides 6' and 6 and in adirection in which an extension of each said inclined side intersects anextension of the other inclined side, said inclined sides forming sidewalls, two short sides 8 and 8' of equal length, each extendingdownwardly on an inclined plane from the other end of the inclined sides7 and 7' in parallel relation to one of the long sides 6 and 6' andbutted end-to-end, said short sides forming a top wall. These sides 6,6', 7, 7', 8 and 8' define the boomerang cross-sectional configurationof the tubular passage. The included angle b is preferably 90° or may beone not very remote therefrom, i.e. 60°-120°, whereby it is possible toavoid any acute angle being present in the cross-sectionalconfiguration.

A multiplicity of long and narrow tubular passages 5 having thisparticular cross-sectional configuration are arranged compactly and inparallel to one another under a systematic alignment to form a tube-nestpassage assembly 9. As can be seen in FIGS. 3 and 4, with respect to oneparticular passage 5A, the center portion of the bottom of the crosssection thereof corresponds with the top side of a passage 5B locatedright thereunder, and the side portions of the bottom of said passage 5Acorrespond with inclined sides of the cross sections of adjacent lowerpassages 5C, 5C. The inclined sides of the cross section of said passage5A correspond with side portions of the bottoms of adjacent upperpassages 5D, 5D. Again, the top side of the cross section of saidpassage 5A corresponds with center portion of the bottom of theimmediate upper passage 5E. Unit assemblies 9 connnected to a suitablesize, are disposed at an angle a to the horizontal. In FIG. 1, saidassemblies, as a tube settler assembly, are generally shown as 2.

The settling performance of a tube settler is greatly improved when thetube passages of the settler are of approximate boomerangcross-sectional configuration. The boomerang cross-sectionalconfiguration has advantages over the commonly used passage shapes: ithas a low hydraulic radius and accordingly the Reynolds number for flowthrough the tubular passages of this invention is low. The boomerangcross-sectional configuration prevents turbulence and permits laminarflow through the passages even where flow rates are much higher.

FIG. 5 gives a comparison of tube settlers of various passage shapes insettling performance, with upward flow rates on abscissae axis andeffluent turbidity on ordinate axis. The geometric and hydraulic valuesof the tube passages tested are shown in Table 1, all passages having asectional area of 36.5 cm².

                  TABLE 1                                                         ______________________________________                                                                          Hydrau-                                                                              Max.                                                Sectional   Passage                                                                              lic dia-                                                                             section                              Test           dimension   length meter  height                               No.  Shape     (cm)        (cm)   (cm)   (cm)                                 ______________________________________                                        A    Circular  Dia.     6.82 61     6.82   6.82                               B    Hexagonal Each     3.75 61     6.48   7.5                                               side                                                           C    Square    Each     6.04 61     6.05   6.04                                              side                                                           D    Rhombus   Each     6.04 61     6.05   8.54                                              side                                                           E    Chevron   Each     5.08 61     4.79   5.08                                              side                                                           F    Similar   Short    3.29 61     5.31   5.08                                    to shape  side                                                                of this                                                                       invention                                                                     Boomerang Oblique  3.59                                                                 side                                                                          Base     6.88                                                  G    Boomerang Oblique  3.59 122    5.31   5.08                                              side                                                                          Base     6.88                                                  ______________________________________                                    

It can be easily seen from FIG. 2 that in the cross section of theapproximate boomerang configuration of this invention, the length of along side 6 is equal to the sum of the length of an inclined side 7 andthe length of a short side 8, and by reducing the proportion of inclinedside 7 it is possible to reduce the sectional area and accordingly toreduce the hydraulic diameter. For the purpose of testing, however, themaximum cross-sectional height for the approximate boomerangconfiguration, which corresponds to the maximum distance a suspendedparticle must fall, was set at 5.08 cm, just equal to that of thechevron cross-sectional configuration, with the result that thehydraulic diameter was 5.31 as against 4.79 for the chevronconfiguration.

Tests were made under the following conditions. Water to be treated wasprepared as follows: To well water at 14° C. was added 50 ppm aluminasulfate, and then soda ash was added to the mixture to obtain pH 7.After pH adjustment, the mixture was added with kaolin so that theturbidity of the water before being introduced into the tube settlers isJIS 100°. Tube settlers of various passage configurations for testingwere arranged at an angle of 60° to the horizontal. At the effluent end,the water collecting section of each settler was connected to a syphone,and measurement was made while controlling the flow rate of waterpassing through the tube passages by changing the height of tube end ofthe syphone. Test water was passed through groups of inclined tubepassages. Operation at each flow rate was maintained for 30 minutes, andafter that, samples of effluent from various tube passages were takenand subjected to turbidity measurement. In FIG. 5, the referencecharacters shown with respect to various lines correspond to the testnumbers in Table 1. According to the test results, the performance ofsquare configuration (C) was most unfavorable, and circular (A),hexagonal (B), and rhombus (D) were slightly better than square (A).Triangular was comparable to said (A), (B) and (D). The chevroncross-sectional configuration (E) and the approximate boomerangcross-sectional configuration (F) of this invention showed far muchbetter results. The approximate boomerang configuration employed in thetest was of somewhat larger hydraulic diameter than the chevronconfiguration tested. This was regarded as a condition unfavorable tothe boomerang configuration tested. Nevertheless, the boomerangconfiguration exhibited somewhat better settling performance than thechevron configuration as is clear from the comparison of performancecurve F with curve E. This reflects the effect of a stagnant flow zonedeveloped by a boundary layer in the acute angle area in the chevrontube passage. On the other hand, the approximate boomerangcross-sectional configuration according to this invention eliminatessuch trouble and permits operation at a high average flow rate. If theboth configurations are tested under same conditions, i.e. samecross-sectional area and same hydraulic diameter, the approximateboomerang configuration of this invention will show more favorablesettling performance.

The tubular passage assembly 9 of above said configuration according tothis invention may be constructed in various ways, but it can bereasonably and economically constructed in manner as described below.

FIG. 6 shows a corrugated sheet 10 of synthetic resin or metal makewhich is a component material for said tubular passage assembly 9.Because of its simple shape, the corrugated sheet 10 may not necessarilybe of costly vinyl chloride or the like which is of low bucklingstrength, and can be produced by shaping ordinary rigid PVC which is oflow cost and has greater strength. The corrugated sheet 10 consists of aseries of alternating small corrugations 11 and large corrugations 12,the former making top walls of the cross-sectional configuration and thelatter making bottom walls. Corrugated sheets 10 are superposed one overanother so that on each small corrugation 11 of a lower sheet is seatedthe backside of a large corrugation 12 of an upper sheet as shown inFIG. 7. Between two sheets superposed, one over the other, are formedtubular passages 5 of approximate boomerang cross-sectionalconfiguration of this invention, each between one surface of contact andanother. A tube nest, that is, tubular passage assembly 9 of desiredsize can be obtained by so superposing adequate number of corrugatedsheets 10 and jointing them together. To have the tubular passages 5disposed at an angle a to the horizon, it is desirable to superpose eachsheet with a shift of a certain distance in lengthwise direction of thecorrugations in relation to the nearest lower sheet. The resultingassembly 9 is of a rhomboid configuration as shown in FIG. 3, and alltubular passages thereof can be of equal length. Jointing and fixing ofcorrugated sheets can be done by using adhesive or adhesive tape, if thesheets are of synthetic resin. Metal corrugated sheets can be easilyjointed or fixed by welding or soldering or by any suitable mechanicalfixing means. Thus, the resulting assembly, as an integralstereo-structure, has high strength and rigidity.

It is clear that said assembly 9 of corrugated construction can beeasily assembled to the desired vertical size by superposing corrugatedsheets according to the designed treating capacity for a tube settler.Crosswise connection of corrugated sheets can be easily made as well inthe following way. FIG. 7 shows two tubular passage assemblies 9 and 9',with side ends thereof placed side by side. The corrugated sheets 10composing the assemblies are designed so that each side end 13 of eachsheet agrees with the bottom end of each large corrugation 12. (SeeFIGS. 4 and 6) Said bottom end is the very point that in the approximateboomerang configuration each two bottom sides meet or butt end-to-end.When corrugated sheets are superposed one over another, a side end 13aof a first alternate sheet forms a side end of the resulting assembly,and a side end 13b of a second alternate corrugated sheet forms thebottom point of a small corrugation 11 (nearest to the assembly end) ofa first corrugated sheet. The opposed side ends of the two assemblies 9are alternately brought into contact so that as shown in FIG. 8, theside end 13a of a sheet layer of the first assembly 9 is butt jointedwith the side end 13b' of a sheet layer of the second assembly 9' andconcurrently the side end 13b of another sheet layer of the firstassembly 9 is butt jointed with the side end 13a' of another sheet layerof the second assembly. In this way, sheet layers of two assemblies areconnected by partial superposition, and if necessary, are bonded orjointed end-to-end. Crosswise connection of tubular passages is thuseffected in orderly manner.

In the above described embodiment, a side end 13 of a corrugated sheet10 agrees with a bottom point of a large corrugation 12. The endingpoint of a side end may be the bottom point of a small corrugation 11 aswell or even a point adjacent to the bottom point of a corrugation andwithin the area of surface contact between an upper sheet and a lowersheet. The end-to-end superposition described above shifts the side endsof said two pairs of sheets crosswise by the sum of half a pitch oflarge corrugation 12 and half a pitch of small corrugation 11. Thus, itis necessary to connect the two assemblies 9 and 9' so that such a shiftcan be compensated between the opposed ends of the assemblies and sothat the sheets butt jointed of the two sheets are enabled to have anadequate area of surface contact adjacent thereto for suitable adhesion.

FIGS. 9 and 10 show another example of side-to-side connection of twotubular passage assemblies 9 and 9'. A side end 13a of a first sheet ofa first assembly 9 is butt jointed to a side end 13a' of a first sheetof a second assembly 9'. In this case, between second sheet ends 13b and13b' of the two assemblies are present a distance corresponding to onepitch of large corrugation 12 plus one pitch of small corrugation 11. Inorder to compensate for said distance, a corrugated strip 14corresponding to one pitch of large corrugation plus one pitch of smallcorrugation as shown in FIG. 10 is prepared and connected to side ends13b and 13b'. If necessary, the corrugated strip is bonded to theassemblies 9, 9' and corrugated sheet 10 on the surface of contactthereto, so as to complete crosswise connection. This connection andbonding can be done, without appreciable difficulty, by precoating thesurface of contact with adhesive, if so required, and inserting acorrugated strip 14 from the influent end of the tubular passages.

This invention can be practised with the following improvements. Forexample, with respect to all tubular passages disposed at an angle b tothe horizon, a short-distance vertical section 15 may be provided asshown in FIG. 11. According to this modification, in the verticalsection the collapse of precipitates and deposits on the inclined bottomsurface in a tubular passage 5 is induced. This phenomenon can beutilized in furthering the slip-off of the precipitates on the bottom.In order to effect such crosswise connection as shown in FIGS. 9 and 10with respect to this modified embodiment, if it is of metal or otherrigid material, it is necessary to insert a corrugated strip 14 of about1/2 length into the passage from the both ends thereof. The presence ofsuch vertical section 15 contributes to the increase of strength andrigidity of the corrugated sheet assembly 9.

Further, it is possible that at the effluent end of the inclined tubepassage assembly 9, an inclined side 7 has no upper end portion and thatas shown in FIG. 12, the top edge of the inclined side 7 is lower thanthe top edges of the bottom side surface 6 and top side surface 8. Withthis type of tube settler, it may happen after a long period of use thatsuspended material sticks to the effluent end of its tubular passage,whereby the effluent end is clogged. Said modified embodiment helpsalleviate such clogging tendency.

According to this invention, the cross section of the tubular passagesconstituting the tube settler gives a uniform height throughout allsections in crosswise direction, except small side-end portions. Thisinsures that the distance which suspended particles in the fluid beingtreated must fall until they reach the bottom of the cross section doesnot exceed a certain value throughout the most part of the cross sectionin crosswise direction. Accordingly, the precipitation of suspendedparticles is substantially uniform throughout the entire area over thebottom. This allows effective utilization of settling area inside thetube passage. Moreover, the bottom side is of V shape and precipitateson the bottom gather in center portion thereof to form thick condensedprecipitate layers. This facilitates the slip-off of precipitates on theinclined plane and decreases the possibility of precipitates beingresuspended in fluids owing to the backflow of fluids, thus resulting insatisfactory separation operation.

The cross section of the tubular passage of this invention has asubstantially lower hydraulic radius than those of commonly used tubepassages. Its hydraulic radius is very close to that of the chevroncross-sectional configuration. This results in a low Reynolds number (anumber expressed as a function of flow rate to geometric dimensions, andaccordingly a high critical flow rate as substantially determined fromthe critical Reynolds number which avoids turbulent flow, a factorpreventing settling of suspended particles (whose rate of settling islow) and which maintains laminar flow. This means increased treatingcapacity and more compact apparatus).

No acute-angle zone is present in the cross-sectional configuration ofthe tubular passage of this invention. Accordingly, there is no risk ofa stagnant flow zone developing due to a boundary layer. This results inincreased average flow rate and virtual gain in treating capacity.

As above described, according to this invention, it is possible toobtain various practical improvements, such as reduced time requirementfor separation, increased clarity of separated fluids, increasedtreating capacity, and provision of more compact apparatus. In addition,the following benefits can be obtained. For example, in cases wherefluids to be treated contain light suspended particles in addition tomaterials having heavier specific gravity than water, or where oilemulsion are to be broken and separated, the surface consisting of thetop sides and inclined sides of the passage cross section serve aseffective separation surface in connection with the floating andseparation of such material. The tubular passage assemblies of thisinvention can be easily fabricated and can be easily bonded andconnected either vertically or crosswise. Assembling and bonding atlocations of equipment can be performed at ease. Transportation in theform of corrugated sheet is possible and this results in low transportcost. The corrugated sheet can be easily made from thin synthetic resinsheet or the like, and therefore resulting tubular passage assembliesare light in weight. The assembly of the invention is of integralstereo-structure and accordingly it has high strength and rigidity.

I claim:
 1. A method of fabricating a tubular passage assembly, whichcomprises the steps of(a) forming a plurality of corrugated sheets, eachhaving a series of alternating large and small corrugations, (b)superposing said corrugated sheets one over another so as to disposeeach backside of large corrugations of an upper sheet in contact with acorresponding small corrugation of a lower sheet, (c) jointing eachcontacting portion of said backside of large corrugations of the uppersheet and said small corrugations of the lower sheet by adhesive fixingmeans to fabricate the tubular passage assembly, and jointing aplurality of said tubular passage assemblies in crosswise direction by(d) disposing the side end of a second alternate corrugated sheet layerin a superposed assembly more inwardly with respect to the axis of theassembly than the side end of a first alternate sheet layer by the sumof half a pitch of large corrugation and half a pitch of smallcorrugation, (e) bringing the side ends of a first assembly intoalternate contact with the side ends of a second assembly so as tobutt-joint one end of a first sheet layer of said first assembly withthe end of a second sheet layer of said second assembly, and likewise tobutt-joint the end of a second sheet layer of said first assembly withthe end of the first sheet layer of said second assembly, and (f)jointing each contacting portion of the first assembly and the secondassembly by adhesive fixing means for jointing the tubular passageassemblies in crosswise direction.
 2. A method of fabricating a tubularpassage assembly, which comprises the steps of(a) forming a plurality ofcorrugated sheets, each having a series of alternating large and smallcorrugations, (b) superposing said corrugated sheets one over another soas to dispose each backside of large corrugations of an upper sheet incontact with a corresponding small corrugation of a lower sheet, (c)jointing each contacting portion of said backside of large corrugationsof the upper sheet and said small corrugations of the lower sheet byadhesive fixing means to fabricate the tubular passage assembly, andjointing a plurality of said tubular passage assemblies in crosswisedirection by (d) disposing the side end of a second alternate corrugatedsheet layer in a superposed assembly more inwardly with respect to theaxis of the assembly than the side end of a first alternate sheet layerby the sum of half a pitch of large corrugation and half a pitch ofsmall corrugation, (e) bringing the side ends of the first assembly intocontact with the side ends of the second assembly so as to butt-jointthe end of a first sheet layer of said first assembly with the end ofsaid first sheet layer of said second assembly, (f) fitting a one-pitchcorrugated strip of large and small corrugations between the side endsof the second sheets of said assemblies, and (g) jointing eachcontacting portion of the said corrugated strip and both assemblies byadhesive fixing means for jointing the tubular passage assemblies incrosswise direction.